Should I show or promise a lower IRR and then over deliver bigger returns or promise higher IRR to attract LPs and investors. I got a mixed reaction from the different LPs

Don't promise anything specific. This is a high-risk asset class. Instead, keep it high level and say something like: "It’s not uncommon for venture funds to target a 3-4x return in a medium scenario and 8x+ in a high scenario." This approach sets realistic expectations without overpromising.